This invention relates to a magnetic medium, such as a thin film magnetic recording medium, and the method of manufacturing the medium. The invention has particular applicability to a magnetic recording medium exhibiting low noise, high coercivity and suitable for high-density longitudinal and perpendicular recording.
The requirements for high areal density impose increasingly greater requirements on magnetic recording media in terms of coercivity, remanent squareness, low medium noise and narrow track recording performance. It is extremely difficult to produce a magnetic recording medium satisfying such demanding requirements, particularly a high-density magnetic rigid disk medium for longitudinal and perpendicular recording. The magnetic anisotropy of longitudinal and perpendicular recording media makes the easily magnetized direction of the media located in the film plane and perpendicular to the film plane, respectively. The remanent magnetic moment of the magnetic media after magnetic recording or writing of longitudinal and perpendicular media is located in the film plane and perpendicular to the film plane, respectively.
A substrate material conventionally employed in producing magnetic recording rigid disks comprises an aluminum-magnesium (Alxe2x80x94Mg) alloy. Such Alxe2x80x94Mg alloys are typically electrolessly plated with a layer of NiP at a thickness of about 15 microns to increase the hardness of the substrates, thereby providing a suitable surface for polishing to provide the requisite surface roughness or texture.
Other substrate materials have been employed, such as glass, e.g., an amorphous glass, glass-ceramic material which comprise a mixture of amorphous and crystalline materials, and ceramic materials. Glass-ceramic materials do not normally exhibit a crystalline surface. Glasses and glass-ceramics generally exhibit high resistance to shocks.
A conventional longitudinal recording disk medium is depicted in FIG. 1 and typically comprises a non-magnetic substrate 10 having sequentially deposited on each side thereof an underlayer 11, 11xe2x80x2, such as chromium (Cr) or Cr-alloy, a magnetic layer 12, 12xe2x80x2, typically comprising a cobalt (Co)-base alloy, and a protective overcoat 13, 13xe2x80x2, typically containing carbon. Conventional practices also comprise bonding a lubricant topcoat (not shown) to the protective overcoat. Underlayer 11, 11xe2x80x2, magnetic layer 12, 12xe2x80x2, and protective overcoat 13, 13xe2x80x2, are typically deposited by sputtering techniques. The Co-base alloy magnetic layer deposited by conventional techniques normally comprises polycrystallites epitaxially grown on the polycrystal Cr or Cr-alloy underlayer. A conventional perpendicular recording disk medium is similar to the longitudinal recording medium depicted in FIG. 1, but does not comprise Cr-containing underlayers.
Conventional methods for manufacturing longitudinal magnetic recording medium with a glass or glass-ceramic substrate comprise applying a seed layer between the substrate and underlayer. A conventional seed layer seeds the nucleation of a particular crystallographic texture of the underlayer.
Conventional Cr-alloy underlayers comprise vanadium (V), titanium (Ti), tungsten (W) or molybdenum (Mo). Other conventional magnetic layers are CoCrTa, CoCrPtB, CoCrPt, CoCrPtTaNb and CoNiCr.
The seed layer, underlayer, and magnetic layer are conventionally sequentially sputter deposited on the substrate in an inert gas atmosphere, such as an atmosphere of pure argon. A conventional carbon overcoat is typically deposited in argon with nitrogen, hydrogen or ethylene. Conventional lubricant topcoats are typically about 20 xc3x85 thick.
The linear recording density could be increased by increasing the coercivity of the magnetic recording medium. However, this objective could only be accomplished by decreasing the medium noise, as by maintaining very fine magnetically noncoupled grains. As the recording areal density increases, conventional magnetoresistive (MR) disks have smaller grain size, which induces superparamagnetic limit and causes the collapse of medium coercivity and magnetic remanance. Also, conventional sputtered media rely on the magnetic alloy composition to increase volume anisotropy.
There exists a need for technology enabling the use of a structure that could increase the medium coercivity by increasing the interfacial anisotropy.
During the course of the present invention, it was found that a multilayer superlattice having a structure with many interfaces of magnetic/non-magnetic layers could increase the medium coercivity by increasing the interfacial anisotropy and the use of Si-containing seedlayer further boosts the coercivity.
The present invention is a magnetic recording medium comprising a substrate, a multilayer superlattice having a structure with many interfaces of magnetic/non-magnetic layers and a Si-containing seedlayer interposed between the substrate and the multilayer superlattice.
An embodiment of the present invention is a method of manufacturing a magnetic recording medium, the method comprising sputter depositing a Si-containing seedlayer on a substrate; and sputter depositing a multilayer superlattice comprising a magnetic layer and a non-magnetic layer.
Another embodiment of this invention is a magnetic recording medium comprising a substrate; a multilayer superlattice comprising a magnetic layer and a non-magnetic layer and a means for boosting the coercivity of the magnetic recording medium. Embodiments of the Si-containing seedlayer include any layer containing Si, including a sputter deposited layer consisting essentially of Si. Embodiments of the means for boosting the coercivity of the magnetic recording medium include, but are not limited to, a layer of a Si-containing material, Pd, CoCr, CrW, NiNb or NiP or a material consisting essentially of Si. In a preferred embodiment, the Si-containing seedlayer is sputter deposited on a soft magnetic underlayer.
Additional advantages and other features of the present invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims. As will be realized, the present invention is capable of other and different embodiments and its several details are capable of modifications in various obvious respects, all without departing from the present invention. The drawings and description are to be regarded as illustrative in nature, and not as restrictive.